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June 6, 2019

Not all stones are created equal

By Advancing the Science contributor

Mayo Clinic’s CT Clinical Innovation Center recently released the first-ever quantitative Stone Analysis Software (qSAS) for characterizing renal stones from CT images. The product is available at no charge for research use through a software sharing agreement.

Cynthia McCollough, Ph.D., Division of Medical Physics, Department of Radiology at Mayo Clinic in Rochester, co-director of Mayo’s CT Clinical Innovation Center and the Brooks-Hollern Professor, says the new software measures the entire volume, shape and size of a renal stone. “A marble and a penny might have a similar diameter at the center, but they’re shaped very differently. Existing standard-of-care technology would not do a good job at describing the differences between stones like these two objects.”

Dr. McCollough says accurate quantification of renal stones is rarely included in a radiology report. “The standard of care is to take a CT scan, draw a line across the stone in one image, use a measurement tool to quantify the diameter, and compare the value to past and future values for the same stone. Hand-drawn measurements aren’t a good way to measure or make decisions because a round stone and an irregularly shaped oblong stone could appear to be the same at the center, yet they represent very different stone burdens to the patient. Qualifiers such as small and big don’t tell the complete picture.

“A stone that’s smooth like a pebble on a beach might pass through the body relatively easily. A rough, spiky stone may be more likely to get stuck in the ureter, be too difficult to pass and require surgery. We can spare the patient the attempt to pass a stone such as that and go directly to surgery.”

The qSAS characterizes every image of the stone, giving its length, width, height, volume, mineral type and roughness. With this higher standard of measurement, physicians can be confident about a stone’s growth from one exam to a subsequent one, according to Dr. McCollough.

Andrea Ferrero, Ph.D., and Cynthia McCullough, Ph.D.

The software, which has been in development at Mayo Clinic for about a decade and has been used to support Mayo researchers, generates fully standardized stone reports in less than five minutes. The only user interaction required is a coarse delineation of the kidneys. After that, the software automatically identifies any renal stones and excludes hardware in the kidneys such as stents and nephrostomy tubes.

Ongoing development in the lab is focused on determining how easy it will be to break up a stone based on what is measured in the CT image. Andrea Ferrero, Ph.D., a recent graduate of the Department of Radiology’s Diagnostic Medical Physicist Residency Program, has been a key driver in preparing the software for release and developing new capabilities such as measuring stone fragility.

“Without Andrea and research technologist Jayse Weaver, we would never have been able to package our various software tools into a comprehensive, user-friendly software product,” says Dr. McCollough. “There is tremendous interest in this software from the renal stone research community.”